Process for producing nano graphene reinforced composite particles for lithium battery electrodes

ABSTRACT

A process for producing solid nanocomposite particles for lithium metal or lithium ion battery electrode applications is provided. In one preferred embodiment, the process comprises: (A) Preparing an electrode active material in a form of fine particles, rods, wires, fibers, or tubes with a dimension smaller than 1 μm; (B) Preparing separated or isolated nano graphene platelets with a thickness less than 50 nm; (C) Dispersing the nano graphene platelets and the electrode active material in a precursor fluid medium to form a suspension wherein the fluid medium contains a precursor matrix material dispersed or dissolved therein; and (D) Converting the suspension to the solid nanocomposite particles, wherein the precursor matrix material is converted into a protective matrix material reinforced by the nano graphene platelets and the electrode active material is substantially dispersed in the protective matrix material. For a lithium ion battery anode application, the matrix material is preferably amorphous carbon, polymeric carbon, or meso-phase carbon. Such solid nanocomposite particles provide a high anode capacity and good cycling stability. For a cathode application, the resulting lithium metal or lithium ion battery exhibits an exceptionally high cycle life.

FIELD OF THE INVENTION

The present invention provides a process for making a nano graphenereinforced composite particle material for use in a lithium ion batteryelectrode (anode or cathode) or in a lithium metal cathode.

BACKGROUND

The description of the prior art will be primarily based on the list ofreferences presented at the end of this section. For convenience, thereferences will be cited with a numerical xx enclosed in a squarebracket, [Ref. xx] or simply [xx].

Concerns over the safety of earlier lithium secondary batteries led tothe development of lithium ion secondary batteries, in which purelithium metal sheet or film was replaced by carbonaceous materials as ananode. There are three fundamentally distinct types of carbonaceousanode materials: (a) graphite, (b) amorphous carbon, and (c) graphitizedcarbon.

The first type of carbonaceous material includes primarily naturalgraphite and synthetic graphite (or artificial graphite, such as highlyoriented pyrolitic graphite, HOPG) that can be intercalated with lithiumand the resulting graphite intercalation compound (GIC) may be expressedas Li_(x)C₆, where x is typically less than 1. In order to minimize theloss in energy density due to the replacement of lithium metal with theGIC, x in Li_(x)C₆ must be maximized and the irreversible capacity lossQ_(ir) in the first charge of the battery must be minimized. The maximumamount of lithium that can be reversibly intercalated into theinterstices between graphene planes of a perfect graphite crystal isgenerally believed to occur in a graphite intercalation compoundrepresented by Li_(x)C₆ (x=1), corresponding to a theoretical specificcapacity of 372 mAh/g.

Carbon anodes can have a long cycle life due to the presence of aprotective surface-electrolyte interface layer (SEI), which results fromthe reaction between lithium and the electrolyte (or between lithium andthe anode surface/edge atoms or functional groups) during the firstseveral charge-discharge cycles. The lithium in this reaction comes fromsome of the lithium ions originally intended for the charge transferpurpose. As the SEI is formed, the lithium ions become part of the inertSEI layer and become irreversible, i.e. they can no longer be the activeelement for charge transfer. Therefore, it is desirable to use a minimumamount of lithium for the formation of an effective SEI layer. Inaddition to SEI formation, Q_(ir) has been attributed to graphiteexfoliation caused by electrolyte/solvent co-intercalation and otherside reactions [Refs. 1-4].

The second type of anode carbonaceous material is amorphous carbon,which contains no or very little micro- or nano-crystallites. This typeincludes the so-called “soft carbon” and “hard carbon.” The soft carbonis a carbon material that can be readily graphitized at a temperature of2,500° C. or higher. The hard carbon is a carbon material that cannot begraphitized even at a temperature higher than 2,500° C. In actuality,however, the so-called “amorphous carbons” commonly used as anode activematerials are typically not purely amorphous, but contain some smallamount of micro- or nano-crystallites. A crystallite is composed of asmall number of graphene sheets (basal planes) that are stacked andbonded together by weak van der Waals forces. The number of graphenesheets varies between one and several hundreds, giving rise to ac-directional dimension (thickness Lc) of typically 0.34 nm to 100 nm.The length or width (La) of these crystallites is typically between tensof nanometers to microns.

Among this class of carbon materials, soft and hard carbons made bylow-temperature pyrolysis (550-1,000° C.) exhibit a reversible capacityof 400-800 mAh/g in the 0-2.5 V range [Refs. 1-3]. Dahn et al. haveprepared the so-called house-of-cards carbonaceous material withenhanced capacities approaching 700 mAh/g [Refs. 1,2]. Tarascon'sresearch group obtained enhanced capacities of up to 700 mAh/g bymilling graphite, coke, or carbon fibers [Ref. 3]. Dahn et al. explainedthe origin of the extra capacity with the assumption that in disorderedcarbon containing some dispersed graphene sheets (referred to ashouse-of-cards materials), lithium ions are adsorbed on two sides of asingle graphene sheet [Refs. 1,2]. It was also proposed that Li readilybonded to a proton-passivated carbon, resulting in a series ofedge-oriented Li—C—H bonds. This provides an additional source of Li⁺ insome disordered carbons [Ref. 5]. Other researchers suggested theformation of Li metal mono-layers on the outer graphene sheets [Ref. 6]of graphite nano-crystallites. The amorphous carbons of Dahn et al. wereprepared by pyrolyzing epoxy resins and may be more correctly referredto as polymeric carbons. Polymeric carbon-based anode materials werealso studied by Zhang, et al. [Ref. 7] and Liu, et al. [Ref. 8].

The following mechanisms for the extra capacity over the theoreticalvalue of 372 mAh/g have been proposed [Ref.4]: (i) lithium can occupynearest neighbor sites; (ii) insertion of lithium species intonano-scaled cavities; (iii) lithium may be adsorbed on both sides ofsingle layer sheets in very disordered carbons containing largefractions of single graphene sheets (like the structure of a house ofcards) [Refs. 1,2]; (iv) correlation of H/C ratio with excess capacityled to a suggestion that lithium may be bound somehow in the vicinity ofthe hydrogen atoms (possible formation of multi-layers of lithium on theexternal graphene planes of each crystallite in disordered carbons)[Ref.6]; and (vi) accommodation of lithium in the zigzag and armchairsites [Ref. 4].

Despite exhibiting a high capacity, an amorphous carbon has a lowelectrical conductivity (high charge transfer resistance) and, hence,resulting in a high polarization or internal power loss. Conventionalamorphous carbon-based anode materials also tend to give rise to a highirreversible capacity due to the existence of too many defect sites thatirreversibly trap lithium.

The third type of anode carbonaceous material is graphitized carbon,which includes meso-carbon microbeads (MCMBs) and graphitized carbonfibers (or, simply, graphite fibers). MCMBs are usually obtained from apetroleum heavy oil or pitch, coal tar pitch, or polycyclic aromatichydrocarbon material. When such a precursor pitch material is carbonizedby heat treatment at 400° to 500°, micro-crystals called mesophasemicro-spheres are formed in a non-crystalline pitch matrix. Thesemesophase micro-spheres, after being isolated from the pitch matrix(pitch matrix being soluble in selected solvents), are often referred toas meso-carbon microbeads (MCMBs). The MCMBs may be subjected to afurther heat treatment at a temperature in the range of 500° C. and3,000° C. In order to obtain a stably reversible capacity in an anode,commercially available MCMBs are obtained from heat-treating mesophasecarbon spheres at a temperature typically above 2,000° C. and moretypically above 2,500° C. for an extended period of time. Graphitizedcarbons have several drawbacks:

-   -   (1) Due to such time-consuming and energy-intensive procedures,        MCMBs have been extremely expensive. Likewise, the production of        all types of graphite fibers (vapor-grown, rayon-based, pitch        based, and polyacrylonitrile-based) is also tedious and        energy-intensive and the products are very expensive.    -   (2) The production of MCMBs having a very small diameter,        particularly 5 μm or less has been difficult. When the        concentration of optically anisotropic small spheres (meso-phase        spheres) increases, the small spheres tend to coalesce and        precipitate to produce bulk mesophase and separation of small        spheres becomes difficult. This is likely the reason why MCMBs        with a bead size less than 5 μm are not commercially available.        Smaller anode active material particles are essential to        high-rate capacity of a lithium ion battery, particularly for        power tool or hybrid vehicle power applications.    -   (3) Furthermore, both MCMBs and graphite fibers give rise to an        anode capacity of typically lower than 350 mAh/g and more        typically lower than 320 mAh/g.

In addition to carbon- or graphite-based anode materials, otherinorganic materials that have been evaluated for potential anodeapplications include metal oxides, metal nitrides, metal sulfides, andthe like, and a range of metals, metal alloys, and intermetalliccompounds that can accommodate lithium atoms/ions or react with lithium.Among these materials, lithium alloys having a composition formula ofLiaA (A is a metal such as Al, and “a” satisfies 0<a #5) are of greatinterest due to their high theoretical capacity, e.g., Li₄Si (3,829mAh/g), Li_(4.4)Si (4,200 mAh/g), Li_(4.4)Ge (1,623 mAh/g), Li_(4.4)Sn(993 mAh/g), Li₃Cd (715 mAh/g), Li₃Sb (660 mAh/g), Li_(4.4)Pb (569mAh/g), LiZn (410 mAh/g), and Li₃Bi (385 mAh/g). However, in the anodescomposed of these materials, severe pulverization (fragmentation of thealloy particles) occurs during the charging and discharging cycles dueto expansion and contraction of the anode active material induced by theabsorption and desorption of the lithium ions. The expansion andcontraction, as well as pulverization of active material particlesresult in loss of contacts between active particles and conductiveadditives and loss of contacts between the anode active material and itscurrent collector. This degradation phenomenon is illustrated in FIG. 1.These adverse effects result in a significantly shortenedcharge-discharge cycle life.

To overcome the problems associated with such mechanical degradation,three technical approaches have been followed in the battery industryand scientific research community:

-   -   (1) Reducing the size of the active material particle        (presumably for the purpose of reducing the strain energy that        can be stored in a particle, which is a driving force for crack        formation in the particle). However, a reduced particle size        implies a higher surface area available for potentially reacting        with the liquid electrolyte.    -   (2) Depositing the electrode active material in a thin film form        directly onto a current collector, such as a copper foil.        However, such a thin film structure with an extremely small        thickness-direction dimension (smaller than 500 nm) implies that        only a small amount of active material can be incorporated in an        electrode, providing a low total lithium storage capacity (even        though the capacity per unit mass can be large).    -   (3) Using a composite composed of small electrode active        particles supported with or protected by a less active or        non-active matrix, e.g., carbon-coated Si particles [Refs.        14-18], sol gel graphite-protected Si, metal oxide-coated Si or        Sn [Ref. 12], and monomer-coated Sn nano particles [Ref. 13].        Presumably, the protective matrix provides a cushioning effect        for particle expansion or shrinkage, as well as prevents the        electrolyte from contacting and reacting with the electrode        active material. Examples of anode active particles are Si, Sn,        and SnO₂. However, all of prior art composite electrodes have        deficiencies in some ways, e.g., in most cases, less than        satisfactory reversible capacity, poor cycling stability, high        irreversible capacity, ineffectiveness in reducing the internal        stress or strain during the lithium ion insertion and extraction        steps, and other undesirable side effects.

For instance, Hung [Ref. 9] disclosed a method of forming a compositeanode material. The steps include selecting a carbon material as aconstituent part of the composite, chemically treating the selectedcarbon material to receive nano particles, incorporating nano particlesinto the chemically treated carbon material, and removing surface nanoparticles from an outside surface of the carbon material withincorporated nano particles. A material making up the nano particlesalloys with lithium. This was a complex process that was not amenable tomass production. Furthermore, the resulting carbon/nanoparticlecomposite anodes did not exhibit any significant increase in capacity,mostly lower than 400 mAh/g, which is not much better than the specificcapacity of graphite.

It may be noted that the coating or matrix materials used to protectactive particles (such as Si and Sn) are carbon [Ref. 14-18], sol gelgraphite [Ref. 19], metal oxide [Ref. 12], monomer [Ref. 13], ceramic[Ref. 10], and lithium oxide [Ref. 11]. These protective materials areall very brittle and/or weak (of low strength). Ideally, the protectivematerial should meet the following requirements: (a) The coating ormatrix material should be of high strength and stiffness so that it canhelp to refrain the electrode active material particles, when lithiated,from expanding to an excessive extent; (b) The protective materialshould also have high fracture toughness or high resistance to crackformation to avoid disintegration during repeated charging-dischargingcycles; (c) The protective material must be inert (inactive) withrespect to the electrolyte, but be a good lithium ion conductor; and (d)The protective material must not provide any significant amount ofdefect sites that irreversibly trap lithium ions. The prior artprotective materials [e.g., Ref. 10-19] all fall short of theserequirements. Hence, it was not surprising to observe that, even withhigh-capacity Si as an anode active material, the resulting anodetypically shows a reversible specific capacity much lower than 1,000mAh/g (based on per gram of the composite material). Furthermore, inmost cases, the electrode was not operated beyond 50 cycles, mostlyfewer than 40 cycles.

Further attempts to improve the capacity and cycling stability of alithium ion battery involved the formation of more complex compositestructures. For instance, Si particles were first coated with a shell ofSiO_(x) and the resulting core-shell structures were then dispersed in acarbon matrix [Ref. 20,21] . Some improvements have been achieved withthis approach, but at the expense of significantly reducing materialprocessing ease. In one case [Ref. 20], the reversible capacity is stilllow (<800 mAh/g) even though the electrode survives 200 cycles. Inanother case [Ref. 21] where a slow and expensive CVD process was usedto prepare the complex structure, a specific capacity of 1,500 mAh/g wasachieved, but only up to 50 cycles.

Complex composite particles of particular interest are (a) a mixture ofseparate Si and graphite particles dispersed in a carbon matrix preparedby J. Yang, et al. [Ref. 22-24] and by Mao, et al. [Ref. 27], (b) carbonmatrix containing complex nano Si (protected by oxide) and graphiteparticles dispersed therein [Ref. 25], and (c) carbon-coated Siparticles distributed on a surface of graphite particles [Ref. 26].Again, these complex composite particles led to a specific capacitylower than 800 mAh/g (for up to 30-40 cycles only) [Ref. 22-24], lowerthan 600 mAh/g (up to 40 cycles) [Ref. 25], or lower than 460 mAh/g (upto 100 cycles) [Ref. 26]. These capacity values and cycling stabilityare not very impressive. It appears that carbon by itself is relativelyweak and brittle and the presence of micron-sized graphite particlesdoes not improve the mechanical integrity of carbon since graphiteparticles are themselves relatively weak. Graphite was used in thesecases presumably for the purpose of improving the electricalconductivity of the anode material. Furthermore, polymeric carbon,amorphous carbon, or pre-graphitic carbon may have too manylithium-trapping sites that irreversibly capture lithium during thefirst few cycles, resulting in excessive irreversibility.

In summary, the prior art has not demonstrated a composite material thathas all or most of the properties desired for use as an anode materialin a lithium-ion battery. Thus, there is an urgent and continuing needfor a new anode for the lithium-ion battery that has a high cycle life,high reversible capacity, low irreversible capacity, small particlesizes (for high-rate capacity), and compatibility with commonly usedelectrolytes. There is also a need for a method of readily or easilyproducing such a material in large quantities. It would be furtherdesirable to have a versatile composite approach that is applicable toboth anode and cathode materials.

REFERENCES

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SUMMARY OF THE INVENTION

For the purpose of increasing the strength, stiffness, and fracturetoughness of a protective matrix (such as carbon) to maintain thestructural integrity of an electrode (either anode or cathode),presumably one can make use of carbon nano-tubes (CNTs) as a primarynano reinforcement additive since CNTs are known to have high strengthand stiffness. However, at this stage of development, CNTs are extremelyexpensive and cannot be produced at a high rate in large quantities. Thehigh costs associated with NGPs have been the primary reason responsibletheir limited uses in industry thus far.

Instead of trying to develop much lower-cost processes for making CNTs,the applicants and co-workers have worked diligently to developalternative nano-scaled carbon materials that exhibit comparableproperties, but are more readily available and at much lower costs. Thisdevelopment work has led to the discovery of processes for producingindividual nano graphene sheets (individual basal plane sheets) andstacks of multiple nano graphene sheets, which are collectively callednano graphene platelets (NGPs). The structures of these materials may bebest visualized conceptually by making a longitudinal scission on thesingle-wall or multi-wall of a nano-tube along its tube axis directionand then flattening up the resulting sheet or plate. In practice, NGPsare obtained from a precursor material, such as minute graphiteparticles, using a low-cost process, but not via flattening of CNTs. Itis important to herein point out that NGPs and CNTs are two totallydifferent classes of materials.

One of the cost-effective processes for NGPs is exfoliation of graphiteto produce graphite worms of loosely connected flakes, followed byseparation of these flakes into isolated (unconnected) nano grapheneplatelets using mechanical means, such as air jet milling,rotating-blade shearing, and ultrasonication. These nano materials arecost-effective substitutes for CNTs or other types of nano-rods forvarious scientific and engineering applications. These diligent effortshave led to several patents or patent applications related to NGPs[Refs. 32-40].

For instance, Jang, et al. [Ref. 33] disclosed a process to readilyproduce NGPs in large quantities. The process includes the followingprocedures: (1) providing a graphite powder containing fine graphiteparticles preferably with at least one dimension smaller than 200 μm(most preferably smaller than 1 μm); (2) exfoliating the graphitecrystallites in these particles in such a manner that at least twographene planes are fully separated from each other, and (3) mechanicalattrition (e.g., ball milling) of the exfoliated particles to becomenano-scaled, resulting in the formation of NGPs with platelet thicknesssmaller than 100 nm. The starting powder type and size, exfoliationconditions (e.g., intercalation chemical type and concentration,temperature cycles, and the mechanical attrition conditions (e.g., ballmilling time and intensity) can be varied to generate, by design,various NGP materials with a wide range of graphene plate thickness,width and length values. We have successfully prepared NGPs with anaverage length in the range of 0.5 to 10 μm). However, the length orwidth can be smaller than 500 nm and, in several cases, smaller than 100nm. Ball milling is known to be an effective process for mass-producingultra-fine powder particles. The processing ease and the wide propertyranges that can be achieved with NGP materials make them promisingcandidates for many important engineering applications. The electronic,thermal and mechanical properties of NGP materials are comparable tothose of carbon nano-tubes; but NGPs are now available at much lowercosts and in larger quantities. Again, NGPs are a new, emerging class ofnano materials that are distinct and different from CNTs.

It is also important to point out that although NGPs can be derived fromnatural or artificial graphite, NGPs and graphite are also different anddistinct classes of materials. Graphite is a poly-crystalline materialcharacterized by a powder structure, wherein each graphite particle iscomposed of multiple graphite crystallites typically with eachcrystallite having both the c-axis dimension, Lc, and the a-axisdimension, La, much greater than 100 nm. These crystallites are randomlyoriented with respect to one another and are loosely bonded togetherwith defected grain-boundary zones. By contrast, NGPs can be as thin asa single atomic plane (also referred to as basal plane or grapheneplane), which has a thickness of approximately 0.34 nm. Thissingle-layer graphene is a building block for several different types ofnano carbon materials (e.g., Fullerene, CNTs and multi-layer NGPs). NGPscan have a thickness up to 100 nm. A multi-layer NGP could be viewed asan ultra-thin single crystal of graphite. The thickness (or number oflayers) of an NGP is a fundamentally important parameter. For instance,although a single-layer NGP is a zero-band gap semi-metal, a two-layergraphene is a semiconductor with a finite band gap. Although asingle-layer graphene is a ferromagnetic material, a double-layergraphene can be an anti-ferromagnetic material, and a multiple-layerNGPs (greater than 3 or more layers) can be paramagnetic. Hence, thethickness of an NGP is not just a geometric parameter, this parameter isan intrinsic material structural feature. Although graphite is arelatively weak and brittle material, nano graphene has been recentlyobserved to exhibit the highest strength among all materials known tothe scientific community [41]. Additionally, nano graphene also exhibitsthe highest thermal conductivity among existing materials [42]. New andunique properties of graphene are emerging on a daily basis. For a quickoverview of this new subject, please refer to [Ref. 43].

After extensive and in-depth research and development efforts, we cameto realize that NGPs (particularly those with a thickness <10 nm,preferably <1 nm) are very effective in enhancing the mechanicalproperties of a protective matrix (such as amorphous carbon or polymericcarbon, polymer, and metal oxide) in a lithium battery electrode.NGP-reinforced protective matrix materials are capable of cushioning thestresses-strains induced to an electro-active particle during lithiuminsertion and extraction (discharge and charge) cycles. Surprisingly,NGPs were found to significantly enhance the structural integrity(strength and fracture resistance) of a range of protective matrixmaterials for electrodes, to the extent that a high specific capacitywas maintained over a much larger number of cycles compared with thoseelectrodes without an NGP-reinforced protective matrix.

Hence, in one preferred embodiment, as schematically shown in FIG. 2(A)and 1(B), the present invention provides a process for producing a nanographene-reinforced nanocomposite solid particle composition containingboth NGPs and an electrode active material dispersed in a protectivematrix. The electrode active material is in the form of dispersed fineparticles (particulates of various shapes, filaments, rods, tubes, andwires, etc.) with a dimension (e.g., diameter) smaller than 1 μm(preferably smaller than 750 nm, further preferably smaller than 500nm). This nanocomposite solid particle composition is preferably in aform of fine particle (preferably <10 μm, more preferably <5 μm, andmost preferably <2 μm) and is most preferably of a spherical orellipsoidal shape. Such a shape is conducive to the formation of anelectrode with a high tap density. A higher tap density means a betterpacking of electro-active material particles that results in a greateramount of active material per unit volume under an identical coating andlaminating condition for electrode fabrication.

In one preferred embodiment, the process for producing solidnanocomposite particles for lithium metal or lithium ion batteryelectrode applications comprise: (A) Preparing an electrode activematerial in a form of fine particles, rods, wires, fibers, or tubes witha dimension smaller than 1 μm; (B) Preparing separated or isolated nanographene platelets with a thickness less than 50 nm; (C) Dispersing thenano graphene platelets and the electrode active material in a precursorfluid medium to form a suspension wherein the fluid medium contains aprecursor matrix material dispersed or dissolved therein; and (D)Converting the suspension to the solid nanocomposite particles, whereinthe precursor matrix material is converted into a protective matrixmaterial reinforced by the nano graphene platelets and the electrodeactive material is substantially dispersed in the protective matrixmaterial.

Specifically, the nanocomposite solid particles may be made by (a)preparing-NGPs from a laminar graphite material (such as naturalgraphite, artificial graphite, MCMB, graphite fiber, and carbon fiber);(b) preparing a precursor (e.g., resin or petroleum pitch) to aprotective matrix material, (c) mixing the NGPs and an electro-activematerial (e.g., Si nano particles, nano-wires, nano-rods, etc) with theprecursor (possibly or optionally in a solvent or liquid medium) to forma suspension, (d) transforming the suspension into droplets (e.g.,forming micron-sized solid particles using, for instance, an atomizationor aerosol formation technique) and removing the solvent; and (e)converting the precursor into the desired protective matrix material(e.g., converting a resin into polymeric carbon via heat treatments).Alternatively, NGPs and electro-active material particles may be mixedwith or coated by a monomer (e.g., a triazine-based compound assuggested by Kim, et al [Ref. 13]), a polymer (e.g., sulfonatedpolyaniline), a ceramic material (e.g., a metal oxide) to form sphericalsolid particles that require no further chemical conversion. In somecases, additional protective material may be coated onto solidparticles, e.g. further coated with an amorphous carbon matrix viachemical vapor deposition.

The matrix material may be selected from a polymer, polymeric carbon,amorphous carbon, meso-phase carbon, coke, petroleum pitch, coal tarpitch, meso-phase pitch, metal oxide, metal hydride, metal nitride,metal carbide, metal sulfide, ceramic, inorganic, organic material, or acombination thereof. Preferably, the protective matrix materialcomprises a carbon material obtained by pyrolyzing or heat-treating apolymer, monomer, organic material, coal tar pitch, petroleum pitch,meso-phase pitch, sugar, glucose, or a combination thereof. The carbonmaterial is lithium ion-conducting. The amount of this carbon materialis preferably reduced by adding a controlled amount of NGPs dispersedtherein. The NGPs serve to reduce the sites in amorphous carbon thatotherwise could irreversibly trap lithium ions or atoms andsignificantly enhance the structural integrity of the carbon matrix.

Typically, the obtained nanocomposite solid particles are substantiallyspherical or ellipsoidal in shape and are of approximately 1-20 μm insize (preferably and usually smaller than 5 μm in diameter or longaxis). For the preparation of an electrode (e.g., anode), thesenanocomposite solid particles are then bonded together with a bindermaterial (e.g., styrene-butadiene rubber, SBR,poly(tetrafluoroethylene), PTFE, or poly(vinylidene fluoride), PVDF), aprocedure similar to the standard procedure in the current practice ofmaking lithium ion batteries. These nanocomposite particles are superiorto meso-carbon micro-beads (MCMBs), conventional fine graphiteparticles, and conventional graphite spherules when used as an anodeactive material for a lithium ion battery. The presently invented solidnanocomposite particles can be readily mass-produced and are of lowcost. Solid particles can be readily made to be smaller than 5 μm if thelength/width of NGPs chosen are smaller than 2 or 3 μm in size and theelectro-active material particles (in a particulate, wire, rod, tube, orfilament form) have a diameter <1 μm. When used as an anode activematerial, they exhibit a high reversible capacity, a low irreversiblecapacity, good compatibility with commonly used electrolytes (nographite layer exfoliation phenomenon and no active material-electrolytereaction), and a long charge-discharge cycle life.

This is in contrast to the situation as proposed by Chan, et al [Ref.28], wherein multiple Si nanowires were catalytically grown from acurrent collector surface in a substantially perpendicular direction, asschematically shown in FIG. 3(A). The electrons produced by the Sinanowires (diameter=89 nm) must travel through the complete nanowirelength, a semiconductor with poor conductivity, to reach the currentcollector. In the nanowire technology of Chan, et al. [28], each Sinanowire is only connected to a current collector through a very narrowcontact area (diameter=89 nm) and, hence, the nanowire would tend todetach from the steel current collector after a few volumeexpansion-contraction cycles. Furthermore, if fragmentation of ananowire occurs (Si is very brittle), only the segment in direct contactwith the steel plate could remain in electronic connection with thecurrent collector and all other segments will become ineffective sincethe electrons generated will not be utilized, as schematically shown inFIG. 3(B).

In the instant invention, the electro-active nanowires or filaments areprotected by a conductive matrix (e.g., carbon), which is preferablyfurther reinforced by NGPs. Even if an electro-active nanowire isfractured into separate segments, individual segments would still remainin physical contact with the conductive matrix or graphene. Theelectrons generated can still be collected. It is also important topoint out that the anode structure of Chan, et al [28] is not compatiblewith the existing practice of making lithium ion battery that involvescoating and laminating anode, separator, and cathode layers throughseveral stages of rolling operations. The vertically grown Si nano-wireswould not survive such a procedure. In contrast, our anode materialrequires no variation in the existing procedures and requires noadditional capital equipment.

The NGPs preferably have a thickness less than 100 nm, and a length,width, or diameter less than 10 μm. The thickness is more preferablyless than 10 nm and most preferably less than 1 nm. The length, width,or diameter of NGPs is preferably less than 5 μm (more preferablysmaller than 2 μm) so that the composite solid particles are typicallyno greater than 10 μm in diameter (preferably smaller than 5 μm). Thiswill allow for facile migration of lithium ions, enabling a high-ratecapacity.

The nano graphene platelets may be obtained from intercalation andexfoliation of a layered or laminar graphite to produce graphite wormscomposed of exfoliated flakes that are loosely interconnected. Theexfoliation is followed by separation of these flakes or platelets. Thelaminar graphite may be selected from a natural graphite, syntheticgraphite, highly oriented pyrolytic graphite, graphite fiber, carbonfiber, carbon nano-fiber, graphitic nano-fiber, spherical graphite orgraphite globule, meso-phase micro-bead, meso-phase pitch, graphiticcoke, or graphitized polymeric carbon. Natural graphite is particularlydesirable due to its abundant availability and low cost. It is desirablethat the nano graphene platelets are prepared prior to beingincorporated into the protective matrix. We have surprisingly found thatgraphite crystallites grown in situ from a carbon matrix (after theanode active particle addition step) during a graphitization treatmentwere not as effective in enhancing the mechanical properties of thecarbon matrix as those externally and separately formed NGPs.Furthermore, once the anode active particles (e.g., Si) are incorporatedin a carbon matrix, a high temperature treatment (e.g., graphitizationfor the formation of internal graphene sheets or graphite crystallites)could induce undesirable reactions (e.g. forming SiC, thus reducing theSi amount).

The electrode active material preferably comprises fine particles, rods,wires, fibers, or tubes with a dimension smaller than 0.5 μm, morepreferably smaller than 200 nm. Most preferably, the electrode activematerial comprises nano particles, nano rods, nano wires, nano fibers,or nano tubes with a dimension smaller than 100 nm.

There is no restriction on the type and nature of the anode activematerial that can be used to practice the present invention. Hence, theanode active material may be selected from the group consisting of:

-   -   a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony        (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), and cadmium (Cd);    -   b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi,        Zn, Al, or Cd with other elements, wherein the alloys or        compounds are stoichiometric or non-stoichiometric;    -   c) oxides, carbides, nitrides, sulfides, phosphides, selenides,        and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Fe, or Cd, and        their mixtures or composites; and    -   d) combinations thereof.

There is also no particular restriction on the type and nature of thecathode active material, which can be selected from, for instance, thegroup consisting of lithium cobalt oxide, doped lithium cobalt oxide,lithium nickel oxide, doped lithium nickel oxide, lithium manganeseoxide, doped lithium manganese oxide, lithium iron phosphate, lithiummanganese phosphate, lithium vanadium oxide, doped lithium vanadiumoxide, lithium vanadium phosphate, lithium transition metal phosphate,lithium mixed-metal phosphates, metal sulfides, metal phosphides, metalhalogenides, and combinations thereof.

Although it is desirable to have a high proportion of electro-activematerial in the solid nanocomposite structure in order to achieve a highlithium storage capacity, this is limited by a minimum amount of thegraphene-reinforced matrix that is needed to cushion the volumeexpansion-induced stresses and strains (and, hence, strain energy). Wehave found that, in order to obtain a balance of high specificreversible capacity, low irreversibility, and long cycle life, thefollowing component proportions are most preferred: nano grapheneplatelets occupy a weight fraction w_(g) of 2% to 50% of the totalnanocomposite weight, the electrode active material occupies a weightfraction w_(a) of 10% to 80% of the total nanocomposite weight, and theprotective matrix material occupies a weight fraction w_(m) of 4% to 30%of the total nanocomposite weight with w_(g)+w_(a)+w_(m)=1.

The present invention also provides a lithium secondary batterycomprising an anode, a cathode, a separator disposed between the anodeand the cathode, and an electrolyte in contact with the anode and thecathode, wherein the anode and/or cathode comprises the aforementionedcomposite solid particles as an anode or cathode active material. Whenthe.anode contains Si as an anode active material, according to apreferred embodiment of the present invention, one can achieve areversible specific capacity of greater than 1,000 mAh/g for longer than500 cycles and, in many cases, even greater than 2,000 mAh/g, calculatedon the basis of the total nanocomposite weight.

In one preferred embodiment of the present invention, the processcomprises (A) Preparing an electrode active material in a form ofnano-rods, nano-wires, nano-fibers, or nano-tubes with a dimensionsmaller than 0.5 μm; (B) On a separate basis, producing a nano fillermaterial, such as nano graphene platelets (NGPs), and (C) Dispersing theelectrode active material and the NGPs in a protective matrix material.Preferably, the electrode active material occupies a weight fractionw_(a) of 10% to 95% of the total nanocomposite weight, and the solidnanocomposite particle is substantially spherical or ellipsoidal inshape. Preferably, the protective matrix material comprises a nanoreinforcement selected from a nano graphene platelet, carbon nano-tube,carbon nano-fiber, or a combination thereof. The protective matrixmaterial preferably comprises polymeric carbon, amorphous carbon, ormesophase carbon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Schematic of a prior art anode active material (e.g., Siparticles) that tends to undergo pulverization during battery cycling.

FIG.2 Two preferred structures of the presently invented solidnanocomposite particles: (A) A spherical nanocomposite particlecomprising electro-active materials (e.g., Si nano particles) and NGPsdispersed in a protective matrix (e.g., amorphous carbon); (B) Aspherical nanocomposite particle comprising electro-active materials(e.g., Si nano-wires) and NGPs dispersed in a protective matrix (e.g.,amorphous carbon);

FIG.3 A prior art anode active material in the form of Si nano-wiresthat were catalytically grown on a surface of a current collector [Ref.28]: (A) Si nano-wires grown vertically and perpendicularly with respectto a steel substrate; (B) Such a configuration is prone to nano-wiredetachment or fragmentation.

FIG.4 The lateral dimensions (average length and width) of NGPs appearto dictate the diameters of the NGP-containing nanocomposite solidparticles after atomization or spray-drying.

FIG.5 The half-cell cycling behaviors of Sample 1 (NGP-reinforced carbonmatrix-protected Si nano particles), Comparative Sample 1a(carbon-protected Si nano particles, no NGPs), and Comparative Sample 1b(carbon-protected, with conventional graphite particle; no NGP).

FIG. 6 Long cycle life of Sample 1.

FIG. 7 Cycling behaviors of Sn particles dispersed in NGP-reinforced andun-reinforced Li₂O matrix.

FIG. 8 Cycling behaviors of Sample 6A (45% Si nanowires, 22% NGPs, and33% carbon matrix, Comparative Sample 6B (approximately 46% Sinanowires, 21% carbon nano-tubes, and 33% carbon matrix) and ComparativeSample 6C (45% Si nanowires and 55% carbon matrix).

FIG. 9 Cycling responses of two lithium ion phosphate-basednanocomposite electrodes.

FIG. 10 Cycling responses of cathode strictures: (1) 88% by weight

-LiV₂O₅ nano-rods, 5% by weight NGPs, and 7% by weight carbon; (2) 88%by weight

-LiV₂O₅ nano-rods and 12% carbon matrix; and (3) bare

-LiV₂O₅ nano-rods only (prepared by mixing the nano-rods with carbonblack (10%) as a conductive additive, bonded with 8% PVDF).

FIG. 11 Cycling responses of three composite materials: (1)Approximately 20% Si (60 nm diameter)+40% graphite+40% carbon; (2)Approximately 20% Si (60 nm diameter)+40% NGPs+40% carbon; and (3)Approximately 20% Si (560 nm diameter)+40% NGPs+40% carbon.

FIG. 12 Fracture toughness (critical stress intensity factor) values ofthree series of carbon matrix composites: (1) carbon matrix reinforcedwith NGPs; (2) carbon matrix reinforced with graphite particles; and (3)carbon matrix reinforced with graphite crystallites in-situ grown from acarbon matrix at high temperatures for extended periods of time.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This invention is related to electrode materials for a high-capacitylithium secondary battery, which is preferably a secondary battery basedon a non-aqueous electrolyte or a polymer gel electrolyte. The shape ofa lithium secondary battery can be cylindrical, square, button-like,etc. The present invention is not limited to any battery shape orconfiguration.

The present invention provides a process of producing a solidnanocomposite particle composition for lithium metal or lithium ionbattery electrode applications. In one preferred embodiment, thecomposition comprises (A) an electrode active material in a form of fineparticles, rods, wires, fibers, or tubes with a dimension smaller than 1μm (e.g., diameter <1 μm); (B) nano graphene platelets (NGPs); and (C) aprotective matrix material reinforced by the NGPs, wherein the NGPs andthe electrode active material are prepared separately and are dispersedin the protective matrix material. In this solid nanocompositecomposition, the NGPs occupy a weight fraction w_(g) of 1% to 90% of thetotal nanocomposite weight, the electrode active material occupies aweight fraction w_(a) of 1% to 90% of the total nanocomposite weight,and the matrix material occupies a weight fraction w_(m) of at least 2%of the total nanocomposite weight with w_(g)+w_(a)+w_(m)=1. Preferably,the solid nanocomposite particle has a substantially spherical orellipsoidal shape with a dimension less than 20 μm, preferably less than10 μm, more preferably less than 5 μm, and most preferably less than 2μm.

The protective matrix material may be selected from a polymer, amonomer, polymeric carbon, amorphous carbon, meso-phase carbon, coke,petroleum pitch, coal tar pitch, meso-phase pitch, metal oxide, metalhydride, metal nitride, metal carbide, metal sulfide, ceramic,inorganic, organic material, or a combination thereof. This protectivematrix material may begin with a precursor material, which is thenphysically or chemically converted to the matrix material. Preferably,the matrix material comprises a carbon material obtained by pyrolyzingor heat-treating a polymer, organic material, coal tar pitch, petroleumpitch, meso-phase pitch, sugar, glucose, or a combination thereof. Thecarbon material may also be obtained from chemical vapor deposition(CVD) or chemical vapor infiltration.

The nano graphene platelets (NGPs) preferably have a thickness less than10 nm and more preferably less than 1 nm. The NGPs may be obtained fromexfoliation and platelet separation of a natural graphite, syntheticgraphite, highly oriented pyrolytic graphite, graphite fiber, carbonfiber, carbon nano-fiber, graphitic nano-fiber, spherical graphite orgraphite globule, meso-phase micro-bead, meso-phase pitch, graphiticcoke, or graphitized polymeric carbon according to any of the proceduresas disclosed in [Ref. 32-40].

In the solid nanocomposite particle composition, the electrode activematerial comprises fine particles, rods, wires, fibers, or tubes with adimension (e.g. diameter) smaller than 1 μm, preferably smaller than 0.5μm, further preferably smaller than 200 nm, and most preferably smallerthan 100 nm. For use in an anode, the electrode active material mostpreferably comprises nano particles, nano rods, nano wires, nano fibers,or nano tubes of silicon, germanium, or tin with a diameter smaller than100 nm. With some protective matrix materials (e.g., carbon reinforcedwith NGPs), sub-micron active particles with a diameter in the range of100 nm and 1 μm are as effective as those <100 nm in providing a highspecific capacity for a long cycle life. However, sub-micron particlescan be less expensive than nano particles (diameter <100 nm).

The solid nanocomposite particle of the present invention may be used inan anode or a cathode. For anode applications, the electrode activematerial comprises an anode active material selected from the groupconsisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb),antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), and cadmium (Cd);(b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al,or Cd with other elements, wherein the alloys or compounds arestoichiometric or non-stoichiometric; (c) oxides, carbides, nitrides,sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb,Bi, Zn, Al, Fe, or Cd, and their mixtures or composites; and (d)combinations thereof. There is essentially no constraint on the type andnature of the anode active material that can be used in practicing thepresent invention.

A useful class of electro-active materials is in the form of nanoscopicwire, also herein referred to as the nanoscopic-scale wire, nanoscalewire, or nanowire. At any point along its length, a nanowire has atleast one cross-sectional dimension and, in some embodiments, twoorthogonal cross-sectional dimensions less than about 500 nm, preferablyless than about 200 nm, more preferably less than about 100 nm, and mostpreferably less than about 50 nm. Where nanoscale wires are described ashaving a core and an outer region, the above dimensions generally relateto those of the core. The cross-section of the nanoscale wire may haveany arbitrary shape, including, but not limited to, circular, square,rectangular, tubular, or elliptical, and may have an irregular shape.For example, ZnO nanowires have a hexagonal cross-section, SnO₂nanowires have a rectangular cross-section, PbSe nanowires have a squarecross-section, and Si or Ge nanowires have a circular cross-section.Again, the term “diameter” is intended to refer to the average of themajor and minor axis of the cross-section. The nanoscale wire may besolid or hollow. The length of the nanoscale wire is preferably at least1 μm and more preferably at least 5 μm. The wires should have an aspectratio (length to diameter) of at least about 2:1 and preferably greaterthan about 10:1.

As used herein, a nanotube (e.g. a carbon nanotube) is generally ananoscopic wire that is hollow, or that has a hollowed-out core,including those nanotubes known to those of ordinary skill in the art.“Nanotube” is abbreviated herein as “NT.” Nanotubes and nano rods may beconsidered as two special classes of small wires for use in theinvention.

Catalytic growth is a powerful tool to form a variety of wire- orwhisker-like structures with diameters ranging from just a fewnanometers to the micrometer range. A range of phases (gas, solid,liquid, solution, and supercritical fluid) have been used for the feederphase, i.e. the source of material to be incorporated into thenano-wire. The art of catalytic synthesis of semiconductor orinsulator-type nano wires from a wide range of material systems havebeen reviewed by Kolasinski [Ref. 29] and by Wang, et al. [Ref. 30].These material systems include Si nanowires (SiNW), heterojunctionsbetween SiNW and CNT, SiO_(x) (a sub-stoichiometric silicon oxide),SiO₂, Si_(1-x)Ge_(x), Ge, AlN, γ-Al₂O₃, oxide-coated B, CN_(x), CdO,CdS, CdSe, CdTe, α-Fe₂O₃ (hematite), ε-Fe₂O₃ and Fe₃O₄ (magnetite),GaAs, GaN, Ga₂O₃, GaP, InAs, InN (hexangular structures), InP, In₂O₃,In₂Se₃, LiF, SnO₂, ZnO, ZnS, ZnSe, Mn doped Zn₂SO₄, and ZnTe. Thesenanowires can be used as anode active materials.

Likewise, there is essentially no constraint on the type and nature ofthe cathode active material provided the active material can be madeinto a fine particle form (e.g., a spherical particle, nano-wire,nano-fiber, nano-rod, or nano-tube) with a dimension smaller than 1 μm.For cathode applications, the electrode active material may comprise acathode active material selected from the group consisting of lithiumcobalt oxide, doped lithium cobalt oxide, lithium nickel oxide, dopedlithium nickel oxide, lithium manganese oxide, doped lithium manganeseoxide, lithium iron phosphate, lithium manganese phosphate, lithiumvanadium oxide, doped lithium vanadium oxide, lithium vanadiumphosphate, lithium transition metal phosphate, lithium mixed-metalphosphates, metal sulfides, metal phosphides, metal halogenides, andcombinations thereof.

In order to strike a balance between the proportion of electrode activematerial (that dictates the lithium storage capacity) and the proportionof NGPs (that provide protection against volume change-induced stressesand strains in a matrix, e.g., carbon matrix), we have conducted anextensive study that covers a wide range of compositions. We have foundthat the most preferred solid nanocomposite particle composition is suchthat NGPs occupy a weight fraction w_(g) of 2% to 50% of the totalnanocomposite weight, the electrode active material occupies a weightfraction w_(a) of 10% to 80% of the total nanocomposite weight, and thematrix material occupies a weight fraction w_(m) of 4% to 30% of thetotal nanocomposite weight with w_(g)+w_(a)+w_(m)=1.

Thus, in one preferred embodiment, the process for producing solidnanocomposite particles comprise: (A) Preparing an electrode activematerial in a form of fine particles, rods, wires, fibers, or tubes witha dimension smaller than 1 μm; (B) Preparing separated or isolated nanographene platelets with a thickness less than 50 nm; (C) Dispersing thenano graphene platelets and the electrode active material in a precursorfluid medium to form a suspension wherein the fluid medium contains aprecursor matrix material dispersed or dissolved therein; and (D)Converting the suspension to the solid nanocomposite particles, whereinthe precursor matrix material is converted into a protective matrixmaterial reinforced by the nano graphene platelets and the electrodeactive material is substantially dispersed in the protective matrixmaterial. It may be noted that NGPs used herein are pre-fabricated priorto being mixed with the electro-active material or the matrix material.These NGPs are not formed during step (C) or step (D).

As an example, such a solid nanocomposite particle may be prepared inthe following way: Graphene platelets, Si nano particles (a preferredanode active material), and a precursor matrix material (e.g., amonomer, oligomer, prepolymer, resin, polymer, coal tar pitch, petroleumpitch, meso-phase pitch, etc) may be blended together and suspended in aliquid to form a precursor suspension or dispersion. The liquid may bethe monomer itself, a solvent for the resin or polymer, or a suspendingmedium, such as water, with a primary purpose of preparing a dispersion.The suspension may then be aerosolized or atomized to form fine aerosolparticles. Concurrently or subsequently, the liquid is removed to formsolid particles that are typically spherical in shape (with a diametertypically less than 10 μm) or ellipsoidal in shape (with a major axisless than 10 μm). This procedure may be accomplished by using an aerosolgeneration, atomization, spray drying, or inkjet printing technique.

It is important to point out that atomization of a mixture of nano orsub-micron-scaled particles, nano graphene platelets, pitch or resin,and a solvent is by no means a trivial task. It is most surprising forus to discover that a mixture or suspension containing more than 10% byweight of NGPs (plus an anode active material, such as Si particles) canstill be handled properly with a pump that delivers the suspension to anatomizer head. A suspension containing 5% by weight of carbon nanotubeswould have a viscosity too high to be processable. We have been able toatomize a mixture containing 75% by weight NGPs, which is a mostimpressive result.

As an optional but preferred procedure, the solid particles generated bythe atomization or aerosol formation procedure are simultaneously orsubsequently subjected to a pyrolyzation (pyrolysis) or carbonizationtreatment to convert the organic or polymeric material into a carbonmaterial. Essentially, one can use a spray pyrolysis technique, such asultrasonic spray pyrolysis or electro-spray pyrolysis, to accomplishboth the aerosol generation and pyrolysis procedures.

Step (D) of converting the suspension comprises a step selected from (a)solidifying a precursor polymer or resin liquid into a solid polymer orresin (e.g., when step (C) involves mixing NGPs and Si particles in apolymer melt); (b) removing a liquid or solvent from the suspension(e.g., in a case where a solvent is used for dissolving petroleum orcoal tar pitch); (c) polymerizing a precursor monomer material; (d)curing a precursor resin to form a solid resin (e.g., curing phenlicresin prior to carbonizing the cured resin); (e) inducing a chemicalreaction to form a protective matrix material (e.g., SnO and Li₃N reactto form Li₂O and Sn wherein Li₂O is the protective material for Snparticles); (f) heat-treating an organic material to form a carbonmatrix material; or a combination thereof. The protective matrixmaterials may be a monomer (e.g., a triazine-based compound as suggestedby Kim, et al [Ref. 13]), a polymer (e.g., sulfonated polyaniline andpolyacrylonitile-co-[methylarylate hexylsulfonic acid] that areion-conducting), or a ceramic material (e.g., a lithium ion-conductingmetal oxide such as Li₂O).

Hence, the present invention provides a process of making grapheneplatelet reinforced matrix nanocomposite composition containing anelectro-active material dispersed therein in a fine particle form. Theactive material can contain fine spherical particles, particles of anyregular or irregular shape, nano-wires, nano-rods, nano-fibers, ornano-tubes. Preferably, the nanocomposite solid particles aresubstantially spherical or ellipsoidal in shape to promote betterpacking during the electrode fabrication procedure (i.e., to increasethe tap density). Further preferably, the solid particles comprisetherein NGP with a thickness of 0.34 nm-10 nm to enhance the structuralintegrity of the resulting anode. The length, width, or diameter of NGPsis preferably less than 5 μm (preferably <1 μm) so that thenanocomposite solid particles are typically no greater than 10 μm indiameter (preferably smaller than 2-5 μm). This will allow for facilemigration of lithium ions.

The solid nanocomposite particles are now new electro-active materials.The preparation procedures of a positive electrode (cathode) or negativeelectrode (anode) from active materials are well-known in the art. Forinstance, the positive electrode can be manufactured by the steps of (a)mixing a positive electrode active material (e.g., the solidnanocomposite particles prepared according to a preferred embodiment ofthe present invention) with a conductor agent (conductivity-promotingingredient) and a binder, (b) dispersing the resultant mixture in asuitable solvent, (c) coating the resulting suspension on a currentcollector, and (d) removing the solvent from the suspension to form athin plate-like electrode.

The original positive electrode active material, for the preparation ofsolid nanocomposite particles, may be selected from a wide variety oflithium-containing oxides, such as lithium manganese oxide,lithium-containing nickel oxide, lithium-containing cobalt oxide,lithium-containing nickel cobalt oxide, lithium-containing iron oxide,lithium-containing vanadium oxide, lithium iron phosphate, etc. Thepositive electrode active material may also be selected from chalcogencompounds, such as titanium disulfate or molybdenum disulfate. Morepreferred are lithium cobalt oxide (e.g., Li_(x)CoO₂ where 0.8≦x≦1),lithium nickel oxide (e.g., LiNiO₂) and lithium manganese oxide (e.g.,LiMn₂O₄ and LiMnO₂) because these oxides provide a high cell voltage.Lithium iron phosphate is also preferred due to its safety feature andlow cost. All these cathode active substances can be prepared in theform of a fine powder, nano-wire, nano-rod, nano-fiber, or nano-tube.They can be readily mixed with NGPs and dispersed in a protective matrix(e.g., carbon) to form a solid nanocomposite particle.

Acetylene black, carbon black, or ultra-fine graphite particles may beused as a conductor agent. The binder may be chosen frompolytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),ethylene-propylene-diene copolymer (EPDM), or styrene-butadiene rubber(SBR), for example. Conductive materials such as electronicallyconductive polymers, meso-phase pitch, coal tar pitch, and petroleumpitch may also be used. Preferable mixing ratio of these ingredients maybe 80 to 95% by weight for the solid nanocomposite particles, 3 to 10%by weight for the conductor agent, and 2 to 10% by weight for thebinder. The current collector may be selected from aluminum foil,stainless steel foil, and nickel foil. There is no particularlysignificant restriction on the type of current collector, provided thematerial is a good electrical conductor and relatively corrosionresistant. The separator may be selected from a synthetic resin nonwovenfabric, porous polyethylene film, porous polypropylene film, or porousPTFE film.

Carbon materials can assume an essentially amorphous structure (glassycarbon), a highly organized crystal (graphite crystal or crystallite),or a whole range of intermediate structures that are characterized byhaving various proportions and sizes of graphite crystallites anddefects dispersed in an amorphous carbon matrix. Typically, a graphitecrystallite is composed of a number of graphene sheets or basal planes(also referred to as a-b planes) that are bonded together through vander Waals forces in the c-axis direction, the direction perpendicular tothe basal plane. These graphite crystallites are typically micron- ornanometer-sized in the a- or b-direction (these are called Ladimension). The c-directional dimension (or thickness) is commonlyreferred to as Lc. The interplanar spacing of a perfect graphite isknown to be approximately 0.335 nm (3.35 Δ). The graphite crystallitesare dispersed in or connected by crystal defects or an amorphous phasein a graphite particle, which can be a flake graphite, carbon/graphitefiber segment, carbon/graphite whisker, or carbon/graphite nano-fiber.In the case of a carbon or graphite fiber segment, the graphene platesmay be a part of a characteristic “turbostratic” structure.

According to a preferred embodiment of the present invention, an anodecomprises nanocomposite solid particles, wherein a solid particle iscomposed of nano graphene platelets (NGPs) and an anode active material(e.g., nano particles of Si, Ge, or Sn) dispersed in a protective matrixmaterial. The NGPs are pre-fabricated using an inexpensive process[e.g., as explained in Refs. 32-40] from an inexpensive startingmaterial, such as natural graphite. For instance, NGPs can be preparedby the following steps: (a) immersing natural graphite particles in amixture of sulfuric acid, sodium nitrate, and potassium permanganate at30° C. to obtain a graphite intercalation compound (GIC); (b) exposingthe GIC to a high temperature (e.g. 600-1,100° C.) for a period of 30seconds to 2 minutes to produce exfoliated graphite; and (c) optionallysubjecting the exfoliated graphite to a graphene sheet separationtreatment, such as air jet milling, ball milling, rotating-bladeshearing, or ultrasonication. In many cases (with adequate intercalationtime and sufficient exfoliation temperature), the exfoliated graphitealready comprises many fully separated nano graphene platelets and,hence, step (c) is not necessary. It may be noted that these NGPs couldcomprise a wide spectrum of graphite-based nano sheets or platelets,including from relatively oxygen-free, pristine graphene sheets tohighly oxidized graphene sheets that are essentially graphite oxide (GO)nano platelets, depending upon the actual NGP process conditions used.

Selected amounts of NGPs and active material particles (e.g., Sinano-wires or Sn nano particles) are then mixed with a precursor matrixmaterial selected from a monomer, prepolymer, polymer, aromatic organic(e.g., polycyclic aromatic molecules such as naphthalene, anthracene,and phenanthrene), petroleum-based heavy oil or pitch, coal-based heavyoil or pitch, meso-phase pitch (e.g., obtained by heat-treating coal tarpitch at 400° C. for a desired period of time), or a combinationthereof. This precursor matrix can be a liquid at room temperature, orheated to an elevated temperature (typically lower than 300° C.) tobecome a liquid. Alternatively, a solvent may be used to dissolve thisprecursor matrix material to form a solution. The liquid or solutionstate facilitates its mixing with NGPs and anode active material to forma suspension or dispersion.

The resulting suspension can be converted into micron-scaled droplets(nanocomposite solid particles) using several approaches. For instance,the suspension may be aerosolized or atomized to form fine aerosolparticles. Concurrently or subsequently, the liquid or solvent isremoved to form solid particles that are typically spherical orellipsoidal in shape with a diameter or major axis less than 10 μm and,in most cases, less than 5 μm if the NGP lateral dimensions are mostlyless than 2 μm. This procedure may be executed by using an aerosolgeneration, atomization, spray drying, or inkjet printing apparatus,which apparatus are well-known in the art. As an optional but preferredprocedure, the solid particles are simultaneously or subsequentlysubjected to a pyrolysis or carbonization treatment to convert theorganic or polymeric material into a carbon material. The heat treatmentof petroleum or coal-based heavy oil or pitch will serve to convert atleast part of the oil or pitch into a meso-phase, an opticallyanisotropic or liquid crystalline phase of a fused aromatic ringstructure. The converted pitch is called a meso-phase pitch. Since NGPsare essentially pure graphite-based or graphene materials, this lowtemperature heat treatment (350-1,200° C.) has no adverse effect on theNGP structure. Essentially, one can use a spray pyrolysis technique,such as ultrasonic spray pyrolysis or electro-spray pyrolysis, toaccomplish both the aerosol generation and pyrolysis procedures.

The NGP/active material-precursor suspension may also be converted intonanocomposite solid particles using combined extrusion, pelletization(granulation), and grinding (including ball milling). Surprisingly, alarge proportion of NGPs and active material can be incorporated into amatrix to form a nanocomposite mixture that is highly flowable(fluid-like) even with an NGP loading as high as 75% by weight in mostof the aforementioned precursor matrix materials. This is likely due totheir two-dimensional, platelet shape, enabling NGPs to readily slideover one another in a liquid medium. Hence, an NGP-containing suspensioncan be extruded into filaments, which are cut into small granules thatare millimeter in size. These granules are then further reduced in sizeusing grinding or ball milling. The resulting micron-scale particles arenot necessarily spherical in shape, but still can be easily bonded by abinder material.

The binder material may also be selected from a polymer, polymericcarbon, amorphous carbon, coal tar pitch or heavy oil, petroleum pitchor heavy oil, meso-phase pitch, metal, glass, ceramic, oxide, organicmaterial, or a combination thereof. In one preferred embodiment, thebinder may be chosen from polytetrafluoroethylene (PTFE), polyvinylidenefluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), orstyrene-butadiene rubber (SBR), for example, as in the cases ofconventional MCMB- or graphite-based anodes. Preferably, the bindermaterial may be a conducting polymer, such as polyacetylene,polypyrrole, polyaniline, polythiophene, and their derivatives.

It may be noted that this new class of nanocomposite solid particles isfundamentally different from MCMBs although the latter contain graphenecrystallites as well (these graphene crystallites were nucleated andgrown in situ directly from the meso-phase matrix duringgraphitization). In contrast, our nano graphene sheets or platelets weremade separately and independently from the carbon formation process andthen added to the carbon matrix along with an electro-active material.MCMBs are typically produced by (a) heating and carbonizing selectedheavy oil or pitch to form meso-phase micro-spheres dispersed in anisotropic matrix pitch; (b) separating the meso-phase micro-spheres fromthe isotropic pitch; and (c) graphitizing the isolated meso-phasemicro-spheres (this latter step being tedious and energy-intensive). TheNGPs in the presently invented nanocomposite solid particles are notobtained by graphitizing the precursor matrix material, as opposed tothe case of conventional MCMB productions. The present solidnanocomposite particle composition contains a high-capacityelectro-active material and, hence, exhibits exceptionally highreversible anode capacity, much higher than that of state-of-the-artMCMBs. Furthermore, NGPs used in the present invention can come fromnatural graphite that is already highly graphitized. One only needs todisperse NGPs in a carbonaceous matrix, along with an electro-activematerial. No graphitization at a high temperature (>2,500° C.) isrequired. The presently invented nanocomposite solid particles and theiranode structures can be very inexpensive.

A wide range of electrolytes can be used for practicing the instantinvention. Most preferred are non-aqueous and polymer gel electrolytesalthough other types can be used. The non-aqueous electrolyte to beemployed herein may be produced by dissolving an electrolytic salt in anon-aqueous solvent. Any known non-aqueous solvent which has beenemployed as a solvent for a lithium secondary battery can be employed. Anon-aqueous solvent mainly consisting of a mixed solvent comprisingethylene carbonate (EC) and at least one kind of non-aqueous solventwhose melting point is lower than that of aforementioned ethylenecarbonate and whose donor number is 18 or less (hereinafter referred toas a second solvent) may be preferably employed. This non-aqueoussolvent is advantageous in that it is (a) stable against a negativeelectrode containing a carbonaceous material well developed in graphitestructure; (b) effective in suppressing the reductive or oxidativedecomposition of electrolyte; and (c) high in conductivity. Anon-aqueous electrolyte solely composed of ethylene carbonate (EC) isadvantageous in that it is relatively stable against decompositionthrough a reduction by a graphitized carbonaceous material. However, themelting point of EC is relatively high, 39 to 40° C., and the viscositythereof is relatively high, so that the conductivity thereof is low,thus making EC alone unsuited for use as a secondary battery electrolyteto be operated at room temperature or lower. The second solvent to beused in a mixture with EC functions to make the viscosity of the solventmixture lower than that of EC alone, thereby promoting the ionconductivity of the mixed solvent. Furthermore, when the second solventhaving a donor number of 18 or less (the donor number of ethylenecarbonate is 16.4) is employed, the aforementioned ethylene carbonatecan be easily and selectively solvated with lithium ion, so that thereduction reaction of the second solvent with the carbonaceous materialwell developed in graphitization is assumed to be suppressed. Further,when the donor number of the second solvent is controlled to not morethan 18, the oxidative decomposition potential to the lithium electrodecan be easily increased to 4 V or more, so that it is possible tomanufacture a lithium secondary battery of high voltage.

Preferable second solvents are dimethyl carbonate (DMC), methylethylcarbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methylpropionate, propylene carbonate (PC), .gamma.-butyrolactone(.gamma.-BL), acetonitrile (AN), ethyl acetate (EA), propyl formate(PF), methyl formate (MF), toluene, xylene and methyl acetate (MA).These second solvents may be employed singly or in a combination of twoor more. More desirably, this second solvent should be selected fromthose having a donor number of 16.5 or less. The viscosity of thissecond solvent should preferably be 28 cps or less at 25° C.

The mixing ratio of the aforementioned ethylene carbonate in the mixedsolvent should preferably be 10 to 80% by volume. If the mixing ratio ofthe ethylene carbonate falls outside this range, the conductivity of thesolvent may be lowered or the solvent tends to be more easilydecomposed, thereby deteriorating the charge/discharge efficiency. Morepreferable mixing ratio of the ethylene carbonate is 20 to 75% byvolume. When the mixing ratio of ethylene carbonate in a non-aqueoussolvent is increased to 20% by volume or more, the solvating effect ofethylene carbonate to lithium ions will be facilitated and the solventdecomposition-inhibiting effect thereof can be improved.

Examples of preferred mixed solvent are a composition comprising EC andMEC; comprising EC, PC and MEC; comprising EC, MEC and DEC; comprisingEC, MEC and DMC; and comprising EC, MEC, PC and DEC; with the volumeratio of MEC being controlled within the range of 30 to 80%. Byselecting the volume ratio of MEC from the range of 30 to 80%, morepreferably 40 to 70%, the conductivity of the solvent can be improved.With the purpose of suppressing the decomposition reaction of thesolvent, an electrolyte having carbon dioxide dissolved therein may beemployed, thereby effectively improving both the capacity and cycle lifeof the battery. The electrolytic salts to be incorporated into anon-aqueous electrolyte may be selected from a lithium salt such aslithium perchlorate (LiClO₄), lithium hexafluorophosphate (LiPF₆),lithium borofluoride (LiBF₄), lithium hexafluoroarsenide (LiAsF₆),lithium trifluoro-metasulfonate (LiCF₃SO₃) and bis-trifluoromethylsulfonylimide lithium [LiN(CF₃SO₂)₂]. Among them, LiPF₆, LiBF₄ andLiN(CF₃SO₂)₂ are preferred. The content of aforementioned electrolyticsalts in the non-aqueous solvent is preferably 0.5 to 2.0 mol/l.

The following examples serve to illustrate the best mode practice of thepresent invention and should not be construed as limiting the scope ofthe invention, which is defined in the claims.

EXAMPLE 1 Preparation of NGPs of Various Sizes from Natural Graphite andProduction of Corresponding NGP-Reinforced Solid Nanocomposite Particles

Natural flake graphite, nominally sized at 45 μm, provided by AsburyCarbons (405 Old Main St., Asbury, N.J. 08802, USA) was milled to reducethe size to approximately 14 μm. The chemicals used in the presentstudy, including fuming nitric acid (>90%), sulfuric acid (95-98%),potassium chlorate (98%), and hydrochloric acid (37%), were purchasedfrom Sigma-Aldrich and used as received. Graphite intercalationcompounds (GICs), which were actually highly oxidized graphite orgraphite oxide (GO) samples, were prepared according to the followingprocedure:

In a typical procedure, a reaction flask containing a magnetic stirringbar was charged with sulfuric acid (1.76 L) and nitric acid (0.90 L) andcooled by immersion in an ice bath. The acid mixture was stirred andallowed to cool for 20 min, and graphite (100 g) was added undervigorous stirring to avoid agglomeration. After the graphite powder waswell dispersed, potassium chlorate (800 g) was added slowly over 25 minto avoid sudden increases in temperature. The reaction flask was looselycapped to allow evolution of gas from the reaction mixture, which wasstirred for 72 hours at room temperature. On completion of the reaction,the mixture was poured into 40 L of deionized water and filtered. The GOwas re-dispersed and washed in a 5% solution of HCl to remove sulphateions. The filtrate was tested intermittently with barium chloride todetermine if sulphate ions are present. The HCl washing step wasrepeated until the test result was negative. The GO was then washedrepeatedly with deionized water until the pH of the filtrate wasneutral. The GO slurry was spray-dried and stored in a vacuum oven at60° C. until use.

Approximately 50 grams of the dried GICs or GO materials were exposed toa thermal shock at 900° C. for 45 seconds in a quartz tube filled withnitrogen gas to obtain an exfoliated graphite sample. Several batches ofthis exfoliated graphite, each of approximately 5 grams, were dispersedin water to form suspensions, which were ultrasonicated at a power levelof 75 watts for several different periods of times: 2 minutes, 10minutes, 30 minutes, 2 hours, and 24 hours. The resulting NGPs wereseparately spray-dried with their average dimensions measured by using acombination of scanning electron microscopy (SEM), transmission electronmicroscopy (TEM), atomic force microscopy (AFM), and specific surfacearea measurements using a BET apparatus.

This series of dried NGP powder samples were then separately mixed withcontrolled amounts of petroleum pitch (A240 from Ashland Oil), toluene(as a solvent or diluent for pitch), and silicon particles (with anaverage diameter of 60 nm) to form a range of separate nanocompositesuspensions. These suspensions were fed into a laboratory scale spraydrier equipped with an atomizer head. This procedure produced relativelyspherical solid nanocomposite particles that are typically micron-scaledwith a relatively narrow particle size distribution. Each solid particlewas composed of three components: Si nano particles, NGPs, and pitchwherein both Si particles and NGPs were well-dispersed in the pitchmatrix. Each of the pitch matrix nanocomposites was heat-treated at 750°C. for two hours to obtain a carbon matrix nanocomposite. In such amulti-phase structure, the otherwise relatively weak pitch carbon matrixwas reinforced by high-strength NGPs and Si serves as an anode activematerial providing a high specific capacity. NGPs by themselves are alsoa good anode active material imparting additional charge storagecapacity. The carbon matrix provides protection against the potentialchemical reaction between Si nano particles and the electrolyte and theinteraction between NGPs and the electrolyte. Furthermore, NGPs serve toreduce the proportion of carbon matrix that otherwise would tend to trapa significant amount of lithium, possibly resulting in a high level ofirreversibility.

The average solid nanocomposite particle size from each suspension wasmeasured and the data was plotted as a function of the corresponding NGPlateral dimension (length or width) in FIG. 4. All samples indicated inFIG. 4 have an NGP proportion of 30% by weight, Si nano particleproportion of 30% and carbon matrix of 40%. This diagram indicates thatthe nanocomposite solid particle diameter scales with the constituentNGP length/width since Si particles are so small (60 nm) and that wecould readily produce nanocomposite solid particles smaller than 5 μm indiameter. Much to our surprise, particles less than 1 μm in diameterwere also readily achievable. This is in sharp contrast to thecommercially available MCMBs that have been limited to particle sizesgreater than 5 μm in diameter. Smaller anode active material particlesare particularly amenable to fast battery charge and dischargeoperations, leading to high-rate capacity batteries.

EXAMPLE 2 Cycling Behaviors of NGP-Containing Nanocomposite, NGP-FreeNanocomposite, and Graphite-Filled Nanocomposite Solid Particle-BasedAnodes (all Containing Si Nano Particles)

In Example 1, a series of samples containing different weight fractionsof Si nano particles (2% to 90%) and different weight fractions of NGPs(2% to 90%) in a carbon matrix (5% to 60%) were prepared.

One of the samples prepared contains approximately 15% NGPs, 60% Si nanoparticles, and 25% carbon matrix and is herein designated as Sample 1.For comparison purpose, a Comparative Sample 1a was prepared bydispersing Si nano particles (approximately 70%) in a pitch matrix, asin Sample 1 but without the presence of the NGP. A Comparative Sample 1bwas prepared by replacing NGPs with fine natural graphite particles(average diameter=3.5 μm) obtained by air-jet milling of natural flakegraphite. FIG. 5 shows the half-cell cycling behaviors of Sample 1,Comparative Sample 1a, and Comparative Sample 1b. It is clear that thesample containing NGPs as a nano reinforcement is far superior to thesample containing no NGPs and the sample containing conventionalgraphite particles instead of NGPs. This is a highly surprising resultsin view of the results of the prior art studies on anode materials basedon Si and graphite particles dispersed in a carbon matrix [Refs. 22-27].The composite particles disclosed in the prior art led to a specificcapacity lower than 800 mAh/g (for up to 30-40 cycles only) [Ref.22-24], lower than 600 mAh/g (up to 40 cycles) [Ref. 25], or lower than460 mAh/g (up to 100 cycles) [Ref. 26]. These capacity values andcycling stability are not nearly as good as what we have achieved (e.g.,FIG. 6). It appears that carbon by itself is relatively weak and brittleand the presence of micron-sized graphite particles does not improve themechanical integrity of carbon since graphite particles are themselvesrelatively weak. By contrast, the anode materials herein developed haveshown a reversible capacity of >2,000 mAh/g (per gram of total compositeweight counting Si, NGP, and C matrix weights) for over 350 cycles.Clearly, NGPs are capable of helping to maintain structural integrity ofa protective matrix, such as carbon, for an anode active material.

As indicated earlier, carbon-coated Si has been investigated as apotential lithium ion battery material, for instance, by T. Umeno, etal. [Ref. 14,15]. They have shown “the excellent electrochemicalperformance of carbon-coated Si as anode materials for lithium-ionbatteries in terms of high reversible capacity over 800 mAh/g, highcoulombic efficiency, good cyclability, satisfactory compatibility withboth the EC and PC-based electrolytes, and better thermal stability thanthat of graphite, etc.” They believed that “carbon-coating in the outerlayer played a very important role in the improvement of theelectrochemical behavior by not only suppressing the decomposition ofelectrolytes on the surface of Si-based electrodes, but also providingintegral and continuous electric contact networks around Si particleseven they are a little expanded after lithium insertion.” However, theseresearchers have indicated that “If the lithiation capacity ofcarbon-coated Si is controlled under 1,200 mAh/g(Si), satisfactorycycleability can be obtained” [Ref. 14]. By contrast, we haveeffectively increased the lithiation capacity to approximately 3,800mAh/g (per gram of Si, corresponding to an alloy of Li_(3.8)Si) and yetstill maintained an outstanding cycling stability when the carbon matrixis reinforced with NGPs.

EXAMPLE 3 NGP Reinforced Nanocomposite Solid Particles (NGPs Preparedfrom Other Laminar Graphite Materials)

NGPs of Samples 3A, 3B, 3C, and 3D were prepared according to the sameprocedure used for Sample 1, but the starting graphite materials werehighly oriented pyrolytic graphite (HOPG), graphite fiber (Amoco P-100),graphitic carbon nano-fiber (from Applied Sciences, Inc., Cedarville,Ohio), and spheroidal graphite (from Hua Dong Graphite Co., Pingdu,China), respectively. Their final interplanar spacings, according tox-ray diffraction data, prior to exfoliation and separation, were 6.6 Å,7.3 Å, 7.3 Å, and 6.6 Å, respectively. They were exposed to anexfoliation temperature of 950° C. for 45 seconds, followed by amechanical shearing treatment using a Cowles rotating-blade apparatusfor 30 minutes. The resulting suspensions or slurries were thensubjected to a drying treatment to obtain NGPs.

The NGPs, along with various proportions of nano Si particles and SnOparticles, were separately mixed with a phenolic resin to form severalmixtures. These mixtures were independently extruded into small diameterfilaments (1-2 mm diameter) using a simple plunger-type device, cured at200° C. for 2 hours, carbonized at 700° C. for 1 hour, chopped intosmall particles, and then ball-milled for 24 hours. The resulting milledparticles are generally irregular in shape with a dimension typicallysmaller than 3 μm. These solid nanocomposite particles are each composedof an electro-active material (Si or SnO), NGPs, and a carbon matrix.

EXAMPLE 4 NGP Reinforced Metal Oxide Nanocomposite Solid Particles

The electro-active particles in Example 4 include materials derived frommetal oxides of the type MO or MO₂, where M=Sn, Pb, Ge, Si, or Cd. As anexample, the active materials may be prepared according to the followingsteps: (1) stanous oxide (SnO) powder and lithium nitride (Li₃N) powderwere mixed in a stoichiometric ratio of two moles of Li₃N to three molesof SnO; (2) the mixture of powders from step (1), along with a selectedamount of NGPs (from Sample 3D), were fed into a planetary ball mill(Model PM-400 from Glen Mills, Clifton, N.J.), and the milling wasproceeded until the reaction between SnO and Li₃N reached a statecharacterized by complete disappearance of the X-ray diffractionpatterns for crystalline SnO and Li₃N, and the subsequent appearance ofthe X-ray patterns for amorphous Li₂O and crystalline Sn. The ballmilling process typically lasts for one to two days at ambienttemperature. The resulting product was a powder mixture containingcrystalline Sn particles dispersed in an amorphous Li₂O matrix, whichwas reinforced by NGPs. The particles are composed of approximately 86%by weight of the Li₂O-Sn mixture and 14% by weight of NGPs. The solidnanocomposite particles were then bonded with 7% resin binder (Sample4). A Comparative Sample 4a was prepared from the Li₂O-Sn mixture powder(without any NGP) bonded with approximately 7% resin binder, along with8% carbon black powder as a conductive additive.

The specific capacity data for Sample 4 and Comparative Sample 4a,summarized in FIG. 7, clearly show that the NGP-reinforced matrix Li₂Ofor Sn particles provides a better cycling stability than thecorresponding Li₂O-protected Sn material system. Although the initialreversible specific capacity, calculated based on the totalnanocomposite weight, was lower (since NGP weight was counted), theNGP-reinforced Li₂O matrix appears to provide a reliable protectionagainst volume change-induced stresses/strains in the Sn particles andcracking of the matrix. In the case of a protective matrix without NGPreinforcement, the specific capacity rapidly degraded ascharge-discharge cycles were repeated.

EXAMPLE 5 Nanocomposites Containing Si_(x)Sn_(q)M_(y)C_(z) TypeElectro-active Materials

The electro-active particles in this example are Si_(x)Sn_(q)M_(y)C_(z)type compositions with (q+x)>(2y+z), x>0, and M is one or more metalsselected from manganese, molybdenum, niobium, tungsten, tantalum, iron,copper, titanium, vanadium, chromium, nickel, cobalt, zirconium,yttrium, or combinations thereof, wherein the Si, Sn, M, and C elementsare arranged in the form of a multi-phase microstructure comprising atleast one amorphous or nanocrystalline phase. As an example, Sample 5awas prepared by ball-milling silicon chips, cobalt powder, and graphitepowder with 28 tungsten carbide balls ( 5/16-inches each, approximately108 grams) for 4 hours in a 45 milliliter tungsten carbide vessel usinga planetary ball mill (Model PM-400 from Glen Mills, Clifton, N.J.)under an argon atmosphere. The vessel was then opened, chunks of cakedpowder were broken up, and the milling was continued for an additionalhour in an argon atmosphere. The temperature of the tungsten carbidevessel was maintained at about 30° C. by air cooling. The product wasdetermined to be approximately Si₇₃Co₂₃C₄. The product in fine powderform was then mixed with a selected proportion of NGPs, phenolic resin,and acetone to make a suspension, which was then subjected to spraypyrolysis to obtain nanocomposite particles. The particles, containingphenolic resin, was then cured at 200° C. for one hour and carbonized at600° C. for two hours to obtain the desired solid nanocompositeparticles as an anode active material.

EXAMPLE 6 Si Nanowire-Based Nanocomposite Particles

In a typical procedure, approximately 2.112 g of silicon powders(average diameter 2.64 μm) were mixed with 80 ml of a 0.1M aqueoussolution of Ni(NO₃).6H₂O and vigorously stirred for 30 min. Then, waterwas evaporated in a rotary evaporator and the solid remnants werecompletely dried in an oven at 150° C. The final sample (Ni-impregnatedSi powers) was obtained by grinding the solids in a mortar.

Subsequently, 0.03 g of Ni-impregnated Si particles were put in a quartzboat, and the boat was placed in a thermal furnace. The sample wasreduced at 500° C. for 4 hours under flowing Ar (180 sccm) and H₂ (20sccm), then the temperature was raised to 990° C. to synthesize Sinanowires.

For the purpose of separating Si nanowires, for instance, every 0.1 g ofthe reacted Si powders were mixed with 10 ml of ethanol and theresulting mixture was sonicated for 1 hour. Subsequently, Si nanowireswere separated from the Si powders by centrifuge at 5000 rpm for 10 min.

Si nanowires were then mixed with controlled amounts of petroleum pitch,toluene, and NGPs to form nanocomposite suspensions. These suspensionswere fed into a laboratory scale spray drier equipped with an atomizerhead. This procedure produced relatively spherical solid nanocompositeparticles that are typically micron-scaled with a relatively narrowparticle size distribution. Each solid particle was composed of threecomponents: Si nanowires, NGPs, and pitch wherein both Si nanowires andNGPs were well-dispersed in the pitch matrix. The pitch matrixnanocomposites were heat-treated at 750° C. for two hours to obtain acarbon matrix nanocomposite with a final composition of approximately45% Si nanowires, 22% NGPs, and 33% carbon matrix (Sample 6A). AComparative Sample 6B was prepared that was composed of approximately46% Si nanowires, 21% carbon nano-tubes (CNTs), and 33% carbon matrix.Another sample, Comparative Sample 6C, was prepared that was composed ofapproximately 45% Si nanowires and 55% carbon matrix.

The cycling responses of these three samples were studied using a halfcell testing configuration in which a Li foil serves as both a referenceand counter electrode and the prepared nanocomposite solidparticle-based electrode as a working electrode. The results aresummarized in FIG. 8. It is clear that the anode materials protected byNGP-reinforced carbon matrix led to a superior cyclic response in termsof high specific capacity and cycling stability (still >1,250 mAh/g, pergram of total composite weight, after an impressive 550 cycles). This iseven better than those of the materials protected by carbon nano-tubes(CNTs), which are much more expensive. However, CNT-reinforcedcarbon-protected electrodes do provide relatively good cyclingresponses, up to 100 cycles (the limit of my patience during thatexperiment). By contrast, the carbon matrix, without a nano filler,provides a limited protection.

EXAMPLE 7 Lithium Iron Phosphate-Containing Nanocomposite Particles forthe Cathode

Lithium iron phosphate LiFePO₄ is a promising candidate cathode materialin lithium-ion batteries for electric vehicle applications. Theadvantages of LiFePO₄ as a cathode active material includes a hightheoretical capacity (170 mAh/g), environmental benignity, low resourcecost, good cycling stability, high temperature capability, and prospectfor a safer cell compared with LiCoO₂. The major drawback with thismaterial has been low electronic conductivity, on the order of 10⁻⁹S/cm². This renders it difficult to prepare cathodes capable ofoperating at high rates. In addition, poor solid-phase transport meansthat the utilization of the active material is a strong function of theparticle size. The presently invented nanocomposite approach overcomesthis major problem by using nano-scaled particles (to reduce the Li iondiffusion path and electron transport path distance) dispersed in acarbon matrix reinforced with NGPs.

Lithium iron phosphate (LiFePO₄) particles were mixed with a selectedproportion of NGPs, phenolic resin, and acetone to make a suspension,which was then subjected to spray pyrolysis to obtain nanocompositeparticles. The particles, containing phenolic resin, was then cured at200° C. for one hour and carbonized at 600° C. for two hours to obtainthe desired solid nanocomposite particles as a cathode active material.The final composition contains approximately 88% by weight lithium ionphosphate nano particles, 5% by weight NGPs, and 7% by weight carbon. Acomparative sample containing approximately 88% by weight lithium ionphosphate nano particles and 12% carbon matrix was also prepared in asimilar manner. Their cycling responses in a half-cell configuration areshown in FIG. 9.

EXAMPLE 8 Preparation of Electro-Active Nano Particles (LiCoO₂-BasedCathode Material)

A micro-emulsion method was used to prepare nano-scaled lithium cobaltoxide particles. Stoichiometric LiNO₃ and Co(NO₃)₂ 6H₂O were dissolvedin water to form an aqueous phase. The salinity of the aqueous phase wasvaried between 1 M and 2 M. The primary component of the oil phase wasanalytical grade cyclohexane. 1-Hexanol [CH₃(CH₂)₆OH] and OP-10[polyoxyethylene octylphenyl ether, 4-(C₈H₁₇)C₆H₄(OCH₂CH₂)_(n)OH, n. 10]were chosen as the surfactant and co-surfactant, respectively. Thevolume ratio of the surfactant to the co-surfactant was adjusted to 3:2.The well-mixed water phase was added to the oil phase with the volumeratio maintained at 1:10. After thorough stirring, a thermodynamicallystable micro-emulsion system was obtained. This micro-emulsion was addeddropwise to the hot oil phase at 200° C. via a peristaltic pump. Theobtained precursors were further dried at 400° C. to remove organicphase. The dried powders were calcined at 850° C. for 2 hours. TheLiCoO₂ particle sizes were found to be between 85 and 150 nm.

The LiCoO₂ particles were mixed with a desired proportion of NGPs,phenolic resin, and acetone to make a suspension, which was thensubjected to spray pyrolysis to obtain nanocomposite particles. Theparticles, containing phenolic resin, was then cured at 200° C. for onehour and carbonized at 600° C. for two hours to obtain the desired solidnanocomposite particles as a cathode active material. The finalcomposition contains approximately 87% by weight lithium ion phosphatenano particles, 5% by weight NGPs, and 8% by weight carbon. Acomparative sample containing approximately 87% by weight lithium ionphosphate nano particles and 13% carbon matrix was also prepared in asimilar manner.

EXAMPLE 9 Preparation of Electro-Active Nano Particles (γ-LiV₂O₅-BasedCathode Material)

A simple and mild solvo-thermal method was used for the synthesis ofγ-LiV₂O₅. In this process, elongated γ-LiV₂O₅ nano particles weresynthesized directly from the solvo-thermal reaction of V₂O₅, LiOH andethanol at 160° C. in an autoclave. Ethanol was employed as a solvent aswell as a reducing agent. In a 50-ml Teflon vessel, 0.02 mol ofanalytically pure LiOH and V₂O₅ were mixed in 40 ml of ethanol. Themixture was subjected to magnetic stirring for 30 minutes. The Teflonvessel containing the mixture was then put into a stainless steelautoclave, which was maintained at 180° C. under autogenous pressure for18 hours. The mixture was then allowed to cool to room temperaturenaturally. The as-formed solid precipitate was filtered, washed withethanol and dried at 100° C. for 2 hours. Transmission electronmicroscopic examinations of the solid precipitate indicates that theγ-LiV₂O₅ particles have a length of 0.3-3 μm and a transverse dimension(diameter) of approximately 30-50 nm. These particles may be called“nano-rods.” Presumably, the reaction can be expressed as follows: 2LiOH+V₂O₅+CH₃CH₂OH→2 γ-LiV₂O₅+CH₃CHO+2 H₂O.

Compared with the conventional preparation methods for γ-LiV₂O₅, thissolvo-thermal method is less expensive and chemically milder. Inparticular, vacuum, argon/nitrogen protected atmosphere, orpost-annealing is not necessary for this simple one-step process. Thisprocess offers a potentially low-temperature, low-cost, andenvironmentally friendly way of producing single-phase, uniform-particlesize, and fine-grained γ-LiV₂O₅ for rechargeable lithium batteries.

The γ-LiV₂O₅ nano-rods were mixed with a selected proportion of NGPs,phenolic resin, and acetone to make a suspension, which was thensubjected to spray pyrolysis to obtain nanocomposite particles. Theparticles, containing phenolic resin, was then cured at 200° C. for onehour and carbonized at 600° C. for two hours to obtain the desired solidnanocomposite particles as a cathode active material. The finalcomposition contains approximately 88% by weight γ-LiV₂O₅ nano-rods, 5%by weight NGPs, and 7% by weight carbon. A comparative sample containingapproximately 88% by weight γ-LiV₂O₅ nano-rods and 12% carbon matrix wasalso prepared in a similar manner. For cycling test purpose, a thirdsample without any carbon protection (bare γ-LiV₂O₅ nano-rods only) wasprepared by mixing the nano-rods with carbon black (10%) as a conductiveadditive, bonded with 8% PVDF as in the other two samples. The testingresults, summarized in FIG. 10, indicate that a protective carbon matrixcan effectively improve the cycling stability of γ-LiV₂O₅ nano-rod-basedcathodes and that the presence of NGPs significantly enhances such aprotection, perhaps by effectively reducing the amount ofirreversibility and suppressing the crack formation.

EXAMPLE 10 Preparation of Electro-Active Nano Particles (LiMn₂O₄-BasedCathode Material)

A particularly useful process involves the insertion of lithium intoelectrolytic manganese dioxide (EMD) in an aqueous medium with glucoseas a mild reductant in open air. The material resulting from calcinationis pure, spinel-structured LiMn₂O₄ particles of sub-micrometric andnanometric size. In one example, the synthesis procedure entaileddissolving 75.4 g of lithium hydroxide (Aldrich) in 3 L ofdouble-distilled water in a 10-L beaker. To this solution, 156.6 g ofEMD was added and the resulting slurry was stirred for 1 hour at 80° C.Then 7.5 g of glucose dissolved in 500 mL of water was added while theslurry was being stirred, which was followed by the addition of 4 L ofwater. The stirring (reaction) was continued further for 8 hours at 80°C. At the end, the reaction slurry was 7.5 L and allowed to cool andsettle for 12 hours. The solid product was washed several times withpure water and then dried at 120° C. The powder was calcined at 775° C.for 24 h in porcelain dishes. The particle sizes of the resultingLiMn₂O₄ were typically in the range of 40-120 nm. Two solidnanocomposite samples were prepared by using a procedure similar to thatin Example 9. The compositions of these two samples are (90% LiMn₂O₄+1%NGP+9% carbon) and (90% LiMn₂O₄+8% NGP+2% carbon). The particles werefound to be mostly spherical or ellipsoidal in shape.

EXAMPLE 11 The Cyclic Responses of Composites Composed of Si NanoParticles (60 nm) or Sub-Micron Particles (560 nm) Dispersed in anNGP-Reinforced Carbon Matrix or Graphite-Reinforced Carbon Matrix

For comparison purposes, spherical nano-Si/graphite/carbon compositepowders were prepared in the following manner: Nano-Si (99.9%, 60 nm)and natural graphite (˜5 μm) powders were mixed in a weight ratio of30:70. The Si and graphite powders were dispersed in a tetrahydrofuran(THF) solution in which a pitch (A500 from Ashland Chemical) as a carbonprecursor was dissolved (solid Si-graphite content of 33 wt. %) and thenvacuum-dried at 100° C. for 6 h. The dried composite was ball-milled for6 hours to prepare the first spherical composite particles. Then, thefirst composite particles and petroleum-based pitch powders were mixedin a weight ratio of 87:13 again in a THF solution, followed bypalletizing (using an atomizer-based spray-dryer in an air atmosphere)and heating under an argon atmosphere at 1,000° C.

Two Si-NGP-carbon composites were prepared as follows: Si particles (60nm and 560 nm in diameter, separately) and NGPs (average thickness=8.9nm) were dispersed in a THF solution in which a pitch as a carbonprecursor was dissolved. The resulting suspension was palletized (usingan atomizer-based spray-dryer in an air atmosphere) and heated under anargon atmosphere at 1,000° C. to obtain solid composite particles ofsubstantially spherical shape (containing Si nano particles) andellipsoidal shape (Sub-micron Si particles with an average diameter of560 nm).

The electrochemical behaviors of these three composite materials wereevaluated and the results in terms of the reversible specific capacityas a function of cycles are plotted in FIG. 11. Two highly significantobservations can be made here. The first is the notion that theNGP-reinforced carbon matrix is more effective than thegraphite-reinforced carbon matrix in terms of serving as a protectingmatrix for Si particles to maintain long-term structural integrity of anelectrode. Although the graphite-reinforced sample performed well duringthe first 50 cycles, its response deteriorated significantly after 70cycles. In contrast, both NGP-protected samples maintain a specificcapacity higher than 700 mAh/g even after 400 cycles. It is ofsignificance to note that ball-milling of graphite particles coulddestruct the particle structure and perhaps sporadically form somegraphite flaks (e.g., >50-100 nm) or even some small amount of nanographene platelets (e.g., <50 nm). But, FIG. 11 clearly showed that thisconfiguration was not good enough to provide long-term protectionagainst electrode deterioration induced by repeated charge and dischargeoperations.

The second observation is that sub-micron Si particles (560 nm)performed as well as the nano-scaled Si particles (60 nm) when under theprotection of an NGP-reinforced carbon matrix. This is significant sincenano-scale particles are typically quite expensive to produce, yetsub-micron particles can be cost-effectively made by techniques such ashigh-intensity ball-milling.

EXAMPLE 12 Fracture Toughness of Carbon, Graphite-Reinforced Carbon, andNGP-Reinforced Carbon Matrix Materials

In order to gain additional insight into the reasons why isolated ordiscrete NGPs prepared prior to being incorporated in a carbon matrixperformed so well in helping to maintain the long-term electrodeintegrity, we decided to measure the fracture toughness or criticalstress intensity factor of three series of composite samples using ASTME399 fracture toughness test. One series of composites contain isolatedNGPs (<10 nm, supplied from Angstron Materials, LLC, Dayton, Ohio) as anano filler or reinforcement. The second series of composites containfine graphite particles (approximately 5 μm) dispersed in a carbonmatrix. The third series of composites were prepared from a petroleumpitch containing some meso-phase domains. Several meso-phase pitchsamples were separately subjected to graphitization treatments (2,000°C. for 1-5 hours and 2,500° C. for 1-2 hours) to grow graphitecrystallites of different weight fractions in situ from the pitchmatrix. Some of these graphite crystallites may be qualified as nanographene platelets since they might have a thickness <50 μm). But, thesegraphene structures are part of a carbon structure and grew out of thecarbon matrix.

The fracture toughness data, an indication of resistance to micro-cracknucleation and growth, are shown in FIG. 12. Although graphite particleswere slightly effective in improving the cracking resistance of carbon,this improvement was diminished when the graphite weight fractionexceeded 30%. This might be due to the difficulty in uniformlydispersing graphite particles. Furthermore, natural graphite particlesare not a high-strength material. Similarly, graphite crystallites grownin situ from a carbon matrix source were not effective in improving thecracking resistance of carbon as well. Such a graphitization treatmentinevitably involves an ultra-high temperature (typically >2,000° C.)that is slow and energy-intensive. Such a high temperature environmentis also conducive to the occurrence of undesirable chemical reactions(e.g., reaction of Si with C to form SiC, reducing the useful amount ofSi).

Quite surprisingly, the isolated NGPs prepared before being added into acarbon matrix provide very impressive enhancement in cracking resistancefor carbon up to 60% by weight of NGPs. This observation appears tofurther assert the notion that isolated NGPs are a totally differentclass of material than carbon and graphite.

In conclusion, we have successfully developed a new and novel class ofsolid nanocomposite particles that are superior lithium batteryelectrode materials. These particles contain an electro-active materialthat has a high lithium storage capacity and a protective matrixmaterial that is reinforced by NGPs. Such a nanocomposite platformtechnology has the following highly desirable features or advantages:

-   -   (1) NGPs are of high strength, high electrical conductivity, and        high thermal conductivity. As a matter of fact, NGPs have been        recently found to exhibit the highest intrinsic strength and        highest intrinsic thermal conductivity among all existing        materials [41,42]. NGPs are a new class of material.    -   (2) A high thermal conductivity implies a high heat dissipation        rate. This is an important feature since the charge and        discharge operations of a battery produce a great amount of        heat. Without a fast heat dissipation rate, the battery cannot        be charged or discharged at a high rate.    -   (3) The high strength of NGPs significantly improves the overall        strength and fracture toughness (resistance to cracking) of a        protective matrix (such as carbon) which is otherwise usually        weak or brittle.    -   (4) The most commonly used protective matrix is carbon which is        not very electrically conductive. NGPs have an electrical        conductivity (up to 20,000 S/cm) that is several orders of        magnitude higher than that of carbon matrix (typically 0.001-1        S/cm).    -   (5) Carbon matrix intrinsically has an excessive amount of        defect sites that irreversibly trap or capture lithium atoms or        ions (would not let go during discharge), thereby significantly        reducing the amount of lithium that can shuttle back and forth        between the anode and cathode. By adding a certain amount of        NGPs, which are themselves an anode active material, one can        effectively reduce the proportion of carbon (hence, reducing the        amount of irreversibility).    -   (6) Although conventional graphite particles (being also an        anode active material) can be added to the carbon matrix to        reduce the amount of the protective carbon, our experimental        data have demonstrated that these graphite particles do not        improve the cracking resistance of carbon. Therefore, the        resulting anode composite materials (e.g., containing Si and        graphite particles dispersed in a carbon matrix) do not provide        a long cycle life. By contrast, by replacing graphite particles        with NGPs that are of much higher strength, we were able to        significantly increase the useful cycle life while maintaining        the reversible capacity at an unprecedented level.    -   (7) Carbon nano-tubes (CNTs) were found to be an effective nano        reinforcement additive for a protective matrix material as well.        But, CNTs remain too expensive at this stage of development. The        NGP-reinforced solid nanocomposite particles of the present        invention can be readily mass-produced and are of low cost.    -   (8) Quite surprisingly, NGP-containing solid nanocomposite can        be readily made into spherical particles having a small diameter        (typically lower than 10 μm, more often lower than 5 μm, and can        be smaller than 1 μm). This is particularly desirable for power        tool and electric vehicle applications where the battery must be        capable of being charged and discharged at a high rate.    -   (9) Further surprisingly, NGP-reinforced protective matrix        materials appear to be capable of effectively cushioning the        large volume changes of electro-active materials such as Si.        When these electro-active materials have a dimension smaller        than 1 μm, they can maintain good structural integrity, under        the protection of a NGP-reinforced matrix, during repeated        charge-discharge cycles. Besides, the matrix itself also becomes        quite resistant to crack initiation and propagation.    -   (10) The present approach is applicable to both the cathode and        anode and, hence, is good for both lithium metal batteries (for        their cathodes) and lithium ion batteries (for anodes and        cathodes).    -   (11) As pointed out earlier, the anode structure of Chan, et al        [Ref. 28] is not compatible with the existing practice of making        lithium ion battery that involves coating and laminating anode,        separator, and cathode layers through several stages of rolling        operations. The vertically grown Si nano-wires would not survive        such a procedure. In contrast, our anode material requires no        variation in the existing procedures and requires no additional        capital equipment.

In summary, the presently invented solid nanocomposite particlessurprisingly impart the following highly desirable attributes to alithium battery electrode: high reversible capacity, low irreversiblecapacity, small particle sizes (for high-rate capacity), compatibilitywith commonly used electrolytes, and long charge-discharge cycle life.

1. A process for producing solid nanocomposite particles for lithiummetal or lithium ion battery electrodes, said process comprising: (A)Preparing an electrode active material in a form of fine particles,rods, wires, fibers, or tubes with a dimension smaller than 1 μm; (B)Preparing separated or isolated nano graphene platelets with a thicknessless than 50 nm; and (C) Dispersing said nano graphene platelets andsaid electrode active material in a protective matrix material to formsaid solid nanocomposite particles, wherein said protective matrixmaterial is reinforced by said nano graphene platelets.
 2. The processof claim 1, wherein Step (C) comprises: (i) Dispersing said nanographene platelets and said electrode active material in a precursorfluid medium to form a suspension wherein said fluid medium contains aprecursor matrix material dispersed or dissolved therein; and (ii)Converting said suspension to said solid nanocomposite particles,wherein said precursor matrix material is converted into said protectivematrix material reinforced by said nano graphene platelets and saidelectrode active material is substantially dispersed in said protectivematrix material.
 3. The process of claim 2, wherein said step ofconverting comprises atomizing or aerosolizing said suspension intosolid nanocomposite particles.
 4. The process of claim 2, wherein saidsolid nanocomposite particles have a substantially spherical orellipsoidal shape.
 5. The process of claim 1, wherein said solidnanocomposite particles are of substantially spherical or ellipsoidalshape with a dimension less than 10 μm.
 6. The process of claim 2,wherein said solid nanocomposite particles are of substantiallyspherical or ellipsoidal shape with a dimension less than 5 μm.
 7. Theprocess of claim 1, wherein said protective matrix material is lithiumion-conducting.
 8. The process of claim 1, wherein said protectivematrix material is selected from a polymer, polymeric carbon, amorphouscarbon, meso-phase carbon, coke, petroleum pitch, coal tar pitch,meso-phase pitch, metal oxide, metal hydride, metal nitride, metalcarbide, metal sulfide, ceramic, inorganic, organic material, or acombination thereof.
 9. The process of claim 2, wherein said step ofconverting said suspension comprises a step selected from (a)solidifying a precursor polymer or resin liquid into a solid polymer orresin; (b) removing a liquid or solvent from said suspension; (c)polymerizing a precursor monomer material; (d) curing a precursor resinto form a solid resin; (e) inducing a chemical reaction to form aprotective matrix material; (f) heat-treating an organic material toform a carbon matrix material; or a combination thereof.
 10. The processof claim 9, wherein said step of heat-treating an organic materialcomprises pyrolyzing or heat-treating a polymer, resin, coal tar pitch,petroleum pitch, meso-phase pitch, coke, sugar, glucose, or acombination thereof to produce a carbon matrix material.
 11. The processof claim 1, wherein said nano graphene platelets have a thickness lessthan 10 nm.
 12. The process of claim 1, wherein said nano grapheneplatelets have a thickness less than 1 nm.
 13. The process of claim 1,wherein said graphene platelets are prepared from exfoliation andplatelet separation of a natural graphite, synthetic graphite, highlyoriented pyrolytic graphite, graphite fiber, carbon fiber, carbonnano-fiber, graphitic nano-fiber, spherical graphite or graphiteglobule, meso-phase micro-bead, meso-phase pitch, graphitic coke, orgraphitized polymeric carbon; and said step of exfoliation and plateletseparation is conducted independent of or separate from said step (A) ofpreparing an electrode active material.
 14. The process as defined inclaim 1, wherein said electrode active material comprises fineparticles, rods, wires, fibers, or tubes with a dimension smaller than0.5 μm.
 15. The process as defined in claim 1, wherein said electrodeactive material comprises fine particles, rods, wires, fibers, or tubeswith a dimension smaller than 200 nm.
 16. The process as defined inclaim 1, wherein said electrode active material comprises nanoparticles, nano rods, nano wires, nano fibers, or nano tubes with adimension smaller than 700 nm but larger than 100 nm.
 17. The process asdefined in claim 1, wherein said electrode active material comprisesnano particles, nano rods, nano wires, nano fibers, or nano tubes ofsilicon, germanium, or tin with a diameter smaller than 100 nm.
 18. Theprocess of claim 1 wherein the electrode active material comprises ananode active material selected from the group consisting of: a) silicon(Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi),zinc (Zn), aluminum (Al), and cadmium (Cd); b) alloys or intermetalliccompounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, or Cd with other elements,wherein said alloys or compounds are stoichiometric ornon-stoichiometric; c) oxides, carbides, nitrides, sulfides, phosphides,selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Fe, or Cd,and their mixtures or composites; and d) combinations thereof.
 19. Theprocess of claim 1 wherein the electrode active material comprises acathode active material selected from the group consisting of lithiumcobalt oxide, doped lithium cobalt oxide, lithium nickel oxide, dopedlithium nickel oxide, lithium manganese oxide, doped lithium manganeseoxide, lithium iron phosphate, lithium manganese phosphate, lithiumvanadium oxide, doped lithium vanadium oxide, lithium vanadiumphosphate, lithium transition metal phosphate, lithium mixed-metalphosphates, metal sulfides, metal phosphides, metal halogenides, andcombinations thereof.
 20. The process of claim 1 wherein said grapheneplatelets occupy a weight fraction w_(g) of 2% to 50% of the totalnanocomposite weight, said electrode active material occupies a weightfraction w_(a) of 10% to 80% of the total nanocomposite weight, and saidmatrix material occupies a weight fraction w_(m) of 4% to 30% of thetotal nanocomposite weight with w_(g)+w_(a)+w_(m)=1.
 21. The process ofclaim 1, further comprising a nano filler selected from a carbonnano-tube, a carbon nano-fiber, or a nano-rod.
 22. A process forproducing solid nanocomposite particles for lithium metal or lithium ionbattery electrode applications, said process comprising: A) Preparing anelectrode active material in a form of nano-rods, nano-wires,nano-fibers, or nano-tubes with a dimension smaller than 0.5 μm; B)Preparing a nano reinforcement selected from a nano graphene platelet,carbon nano-tube, carbon nano-fiber, or a combination thereof; and C)Dispersing said electrode active material and said nano reinforcement ina protective matrix material to form said solid nanocomposite particlesthat are substantially spherical or ellipsoidal in shape.
 23. Theprocess of claim 22, wherein said protective matrix material comprisespolymeric carbon, amorphous carbon, or meso-phase carbon.
 24. Theprocess of claim 22, wherein said solid nanocomposite particles have adimension less than 5 μm.
 25. The process of claim 22, wherein saidprotective matrix material is selected from a polymer, polymeric carbon,amorphous carbon, meso-phase carbon, coke, petroleum pitch, coal tarpitch, meso-phase pitch, metal oxide, metal hydride, metal nitride,metal carbide, metal sulfide, ceramic, inorganic, organic material, or acombination thereof.